International Operations

ARINC 424 Shorthand System

ARINC-424 Shorthand Lat/Long Hemispheres, from Eddie's notes.

Eddie Sez:

It is an elegant idea but that isn't the point. Your FMS uses these oceanic codes to represent various points around the globe so you need to know how to decode the code. Your approach plates use the VOR/DME codes to identify some of the waypoints. Once you've understand how the points are built, you will be able to crosscheck what is on your screen with reality. Note there has been a change to the specification in the North Atlantic to allow for half-degree latitude spacing. This was first implemented in 2014 by moving the "N" a few spaces but so many pilots were misplacing the "N" that they suspended the change for a year. It looks like it is back, using an "H" but as of June 2015 the change is just finding its way into FMS coding. You should always double check the coding translates into the correct latitude and longitude. If you are assigned a waypoint using half-degree latitudes, especially so.

The specification itself comes these days from Rockwell-Collins, costs $504.00, and covers a lot more than what you as a pilot needs. You can, however, piece together the important stuff from other sources, which I've done below.

What follows comes from the references shown below. Where I think it helpful, I've added my own comments in blue.

Oceanic Waypoints

The following comes from a Gulfstream manual but it describes the ARINC 424 specification for naming oceanic waypoints. If your aircraft uses this specification, these codes should work for you. Note: most FMS do not employ a code for every single latitude/longitude combination to safe database space, just the more popular ones. The manual didn't consider half degree waypoints. More on that later.

These waypoints are named according to ARINC 424 navigation database specification

Southern hemisphere uses the letters S or W

Northern hemisphere uses the letters N or E

Latitude always proceeds longitude

Only the last two digits of longitude are used

Placement of the letter designator (N, S, E, W) in the string of five characters indicates the value of the longitude one-hundredths digit

The letter in the last position indicates longitude is less than 100

The letter in the third position indicates longitude is 100 or greater

Letter

Lat

Lon

N

North

West

E

North

East

S

South

East

W

South

West

Examples:

N 52 00/W 075 00 = 5275N

N 75 00/W 170 00 = 75N70

S 50 00/E 020 00 = 5020S

N 50 00/E 020 00 = 5020E

S 52 00/W 075 00 = 5275W

Half-degree waypoints are used in parts of the North Atlantic and the ARINC-424 code has been changed a few times as a result. The latest version is based on an ICAO NAT OPS Bulletin and reported in the following Jeppesen letter.

Jeppesen will add Half Degree Grid Waypoints in the Gander and Shanwick Oceanic Control Areas (OCAs) according to section 2 of the ICAO NAT OPS Bulletin beginning in NavData cycle 1510, effective 17 September 2015. Half Degree Grid Waypoints for all other North Atlantic Regions will be added on or after NavData cycle 1512.

Jeppesen will use the Identifier Naming Convention provided in section 5.3 of the bulletin, which states: “Hxxyy, where xx = degrees and 30 minutes of NORTH latitude and yy = degrees of WEST longitude (e.g., H5250 = 52o30’ NORTH 050o00’ WEST).”

Photo: Half-degree waypoint examples, from Eddie's aircraft.

As you can see from the photo, the half-degree inputs do indeed work. In the photo below you see the results.

Oceanic ARINC 424 Example

Figure: Example Master Document, Oceanic, from Eddie's notes.

In the example master document we see a series of waypoints written in the ARINC 24 code: 5150N 5240N 5230N 5220N

The pilot recorded the oceanic clearance as given using the more conventional format: 51° North, 50° West, and so forth.

Eddie's Lawyer Advises:

Always remember that Eddie, when you get right down to it, is just a pilot. He tries to give you the facts from the source materials but maybe he got it wrong, maybe he is out of date. Sure, he warns you when he is giving you his personal techniques, but you should always follow your primary guidance (Aircraft manuals, government regulations, etc.) before listening to Eddie.

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